Reduction technique for permanent magnet motor high frequency loss

ABSTRACT

A system including a motor loss reducing controller system utilizing input band-shifting, an integral control architecture and inverse band-shifting is disclosed. The motor loss reducing controller system may provide correction of harmonic currents flowing to a PM motor from a motor controller. The compensation is added to the PWM voltage command signals. Within a compensator, d-axis and q-axis current feedback signals are frequency shifted down by n times the fundamental frequency. This converts the initial motor stationary harmonic currents into DC values. The frequency shifting is completed by multiplying the feedback signal by sine and cosine carrier signals of the shifted frequency. An integral controller may cancel any component of error at a desired DC value. An inverse frequency-shift transformation is applied to the output of the I controller in order to shift the command output signal back to the original reference frame.

FIELD

The present disclosure relates to automatic control system design, andmore particularly, to systems and methods of motor loss reduction.

BACKGROUND

Conventional motor current controllers utilize a control loop feedbackarchitecture. For instance, a proportional-integral-derivative PIDcontroller may calculate an error value as the difference between ameasured process variable and a desired set point/control variable. Aproportional-integral (PI) controller may share some of thefunctionality as the functionality of a PID controller. High speedpermanent magnet motors may experience high frequency rotor losses.

SUMMARY

The present disclosure relates to a system including a motor lossreducing controller system utilizing input band-shifting by adisturbance frequency, an integral control architecture and outputinverse band-shifting and phase delay compensation by the disturbancefrequency. The controller system may eliminate errors and/or takecontrol action based on past and present control errors at thedisturbance frequency. The feedback signal may be multiplied by the sineof the theta position of the frequency of interest and the feedbacksignal may be multiplied by the cosine of the theta position of thefrequency of interest. Stated another way, the initial feedback signalis parsed into sine and cosine components at a particular frequency.This effectively band-shifts the feedback signal for treatment by thecontroller.

According to various embodiments, a system including a motor lossreducing controller system utilizing input band-shifting, an Integralcontrol architecture and inverse band-shifting is disclosed. The motorloss reducing controller system may provide correction of harmoniccurrents flowing to a motor, such as a permanent magnet (PM) motor froma motor controller. The compensation is added to the pulse widthmodulated voltage command signals. Within a compensator, d-axis andq-axis current feedback signals are frequency shifted down by n timesthe fundamental frequency. N may be an integer or non-integer value.This converts the initial motor stationary harmonic currents into DCvalues. The frequency shifting is completed by multiplying the feedbacksignal by sine and cosine carrier signals of the shifted frequency. Anintegral controller may cancel any component of error at a desired DCvalue. An inverse frequency-shift transformation is applied to theoutput of the I controller in order to shift the command output signalback to the original reference frame.

According to various embodiments, a system comprising a motor losscontroller structure configured motor loss reduction, comprising aninput bandshifting stage, an integral controller stage, and an outputinverse bandshifting with phase compensation stage are disclosed. Theinputs to the system may be a feedback signal, a motor frequency signaland/or a control value. The sine of an angular component of the motorfrequency signal may be multiplied by the feedback signal in the inputbandshifting stage to form a first band-shifted feedback signal. Thecosine of the angular component of the motor frequency signal may bemultiplied by the feedback signal in the input bandshifting stage toform a second band-shifted feedback signal. Errors in the firstband-shifted feedback signal and the second band-shifted feedback signalare cancelled via integral control in the I controller stage. An inversefrequency-shift transformation is applied to the output of the Icontroller stage in the output inverse bandshifting stage.

According to various embodiments a motor loss controller configured toband-shift a motor frequency signal by a multiple of a fundamentalfrequency into parsed sine and cosine components and multiply a feedbacksignal by each of the sine and cosine components is described herein.The motor loss controller may perform integral control of a controlvalue band-shifted sine component and a control value band-shiftedcosine component. The performing integral control may eliminate and/orreduce a disturbance on the output of the system by rejecting a DCdisturbance in a band-shifted control value. The motor loss controllermay inverse band-shift the sine component back to its original band. Themotor loss controller may inverse band-shift the cosine component backto its original band. The motor loss controller may sum the inverseband-shifted sine component and the inverse band-shifted cosinecomponent together to result in a controller output.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements.

FIG. 1 depicts a representative structure of a feedback controller, inaccordance with various embodiments;

FIG. 2 depicts a representative current controller structure showing thed and q axis PI controllers for conventional current regulation inconjunction with motor loss controllers coupled in parallel, inaccordance with various embodiments;

FIG. 3 depicts a loop gain and phase in accordance with variousembodiments; and

FIG. 4 depicts a loop gain and phase compensation set to 90° phase leadphase compensation at 1 kHz, in accordance with various embodiments.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration and their best mode. While these exemplary embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the disclosure, it should be understood that other embodimentsmay be realized and that logical changes may be made without departingfrom the spirit and scope of the disclosure. Thus, the detaileddescription herein is presented for purposes of illustration only andnot of limitation. For example, the steps recited in any of the methodor process descriptions may be executed in any order and are notnecessarily limited to the order presented. Furthermore, any referenceto singular includes plural embodiments, and any reference to more thanone component or step may include a singular embodiment or step.

The present disclosure relates to the design of a feedback controllerfor reducing motor loss, where the controller is configured for DCregulation of a control quantity as well as rejection (such as acomplete rejection) of a disturbance at a known frequency. According tovarious embodiments, controller disclosed herein may be configured to,and/or utilized to, address this disturbance at the known frequency.

According to various embodiments and with reference to FIGS. 1 and 2, acontroller configured to reduce high frequency rotor losses in a highspeed permanent magnet motor is disclosed herein. The motor losscontroller system 101 applies a compensation of current ripple at thefifth and seventh harmonic frequencies of a fundamental frequency on theAC side of a DC to AC inverter. The motor loss controller system 101compensates for the fifth and seventh harmonic currents that areotherwise present on the AC output of the inverter flowing to theconnected motor, thereby reducing losses in the inverter (e.g., thetransistors, diodes and/or magnetics of the inverter), the feedersconnecting the inverter and motor, and in particular, the motor.

In high speed PM motors connected to motor controller inverters,significant motor losses are commonly present due to fifth and seventhharmonic frequency power quality current distortions. Aerospace motorsmay operate at high speeds, for instance, at 1300 Hz. Thus, the fifthand seventh harmonic currents may be a high frequency value (e.g., 6500and 9100 Hz). At these frequencies, eddy current rotor losses, statorlamination losses, rotor lamination losses, and skin effect losses mayresult in increased motor heating and thermal issues. Since motor eddycurrent and hysteresis losses increase at approximately the square ofthe frequency and the square of current amplitude, significant motorlosses are produced due to the fifth and seventh harmonic currents.

According to various embodiments, a controller configured to correctfifth and seventh harmonic currents flowing to a PM motor from a motorcontroller are disclosed herein. The compensation is added to the pulsewidth modulated (PWM) voltage command signals. Within the controller,d-axis and q-axis current feedback signals are frequency shifted down bya multiple of the fundamental frequency, such as six times thefundamental frequency. This converts the initial motor stationaryreference frame fifth harmonic currents and seventh harmonic currentsinto DC values. The frequency shifting is completed by multiplying thefeedback signal by sine and cosine carrier signals of the shiftedfrequency. After this transformation, any disturbance at six times thefundamental in the d-axis and q-axis currents are transformed to DCvalues. Notably, in response to integral control, the fifth and seventhharmonics of the motor current are transformed into a sixth harmonicfrequency in the DQ reference frame. Thus, in response to control and/orelimination of the sixth order harmonic distortion in the DQ referenceframe, the fifth and/or seventh order harmonics in the actual motorcurrents are effectively eliminated. Thus, motor loss controller system101 may be configured to eliminate distortion in the DQ axes at sixtimes the fundamental frequency.

According to various embodiments, integral control may be utilized tocompletely cancel any component of error at DC (i.e. the errororiginally at the stationary fifth and seventh harmonics and at thesixth d-axis and q-axis harmonics). An inverse frequency-shifttransformation is applied to the output of the I controller 200 stage inorder to shift the command output signals back to the original referenceframe.

The present motor loss controller system 101 comprises phasecompensation added to the output inverse band-shifting stage 300 tocompensate for phase lag between PWM control signals and the resultantchange in the motor current. The phase compensation assists withstabilization of the motor loss controller where it would otherwise nothave phase margin and would thus be unstable. Since the transformationsand integral control are limited to affecting the loop gain of the motorloss controller system 101 at and near the frequency of the frequencyshifting, the phase delay characteristics of the motor loss controllersystem 101 remain unchanged at frequencies which are a sufficientdistance from the band-shifting frequency (see FIGS. 3 and 4).

Traditionally, controllers have been designed to regulate to a constantset point value, such as controlling a motor speed at a substantiallyconstant 10,000 rpm. Proportional integral type controllers are wellsuited for holding steady the average value rate of the command, (e.g.10,000 rpm); however, for systems having a reoccurring disturbance (suchas current distortions causing motor loss), a proportional integral typecontroller is not able to eliminate the disturbance. In manycircumstances, it is preferable that the oscillation be reduced oreliminated. Among other attributes, the controller disclosed hereinprovides an approach for eliminating and/or reducing that oscillation(e.g. a disturbance, such as a sinusoidal disturbance, at a knownfrequency).

According to various embodiments, and with reference to FIG. 1, thestructure of a motor loss controller system 101 utilizing inputband-shifting stage 100, I controller 200 stage and output inverseband-shifting stage 300 is disclosed. The inputs to the motor losscontroller system 101 may include a control value 25, such as zero, afeedback signal 75, and an input at the motor frequency, which is aknown frequency. The inputs to the motor loss controller system 101 mayfurther include a phase shifting component as described further below.Depicted by representative multiplier box 150, the feedback signal maybe multiplied by the sine of the ω(t) angular position of the integralof six times the motor frequency signal.

Direct-quadrature transformation is a mathematical transformation thatrotates the reference frame of three-phase systems in an effort tosimplify the analysis of three-phase circuits. The direct-quadraturetransformation can be thought of in geometric terms as the projection ofthe three separate sinusoidal phase quantities onto two axes rotatingwith the same angular velocity as the sinusoidal phase quantities. Thetwo axes are called the direct, or d, axis; and the quadrature or q,axis; that is, with the q-axis being at an angle of 90 degrees from thedirect axis.

The inputs to the controller are the d or q axis feedback currents andthe motor frequency. The controller reduces current distortion at 6times the fundamental frequency in the d and q reference frame. Only thed-axis controller is shown (a virtually identical controller is used inthe q-axis) in FIG. 1. A phase lead (see φ component 260 on FIG. 1) maybe added to the output sine and cosine operation for a harmonic ofinterest, such as the sixth order harmonics, to compensate for plantbehavior (for instance a 90 degree lead angle to compensate inductor lagbetween applied voltage and resultant current).

Depicted by representative multiplier box 160 the feedback signal may bemultiplied by cosine of six times the ω(t) angular position of theintegral of the motor frequency. Stated another way, the initialfeedback signal is parsed into sine and cosine components at an integralof a particular frequency. This effectively band-shifts the feedbacksignal for treatment by the motor loss controller.

In the frequency domain, the feedback signal is shifted (e.g., down orup) by the determined frequency ω, generally speaking, such that thedisturbance oscillation becomes a DC quantity. The I controller 200stage is configured to eliminate that disturbance because thedisturbance is now at a DC level and can be eliminated by a I controller200 stage. The six times ω(t) angular position of the integral of themotor frequency may be summed 250 with a phase lead 260 to compensatefor phase delay. For instance, if at the sixth harmonic of the motorfrequency has a 100 degree phase leg at the output of the system ascompared to the motor frequency input, 100 degrees of phase delaycompensation may be introduced to the system. Thus, the motor losscontroller system 101 compensates for phase leg in the inverseband-shifting stage.

The motor loss reduction controller may be configured to act on theband-shifted (down) frequency signal to eliminate the disturbance ofinterest, such as the sixth order harmonic. The output inverseband-shifting stage 300 transforms the band-shifted treated signal backto the original frequency of the feedback signal. Stated another way,via integral control action, the I controller is able to reject, forexample to perfectly reject, any DC disturbance at the I controllerinput, which therefore likewise rejects (due to input band-shifting andoutput inverse band-shifting) the AC disturbance that was present atfeedback signal 75, at the six times motor frequency contained inintegrated phase shifted motor frequency signal 50. The integral gaincontrol output of the I controller 200 stage is multiplied with the sinecomponent and the cosine component of the integrated phase shifted motorfrequency signal 50. The outputs are summed together by a summer 350 andtransmitted as an output as the controller output 95.

According to various embodiments and with reference to FIG. 2, a currentcontroller structure showing the d and q axis PI controllers forconventional current regulation in conjunction with motor losscontroller system 101 of FIG. 1 is shown.

According to various embodiments and with reference to FIG. 3, the loopgain and phase of an embodiment of motor loss controller system 101. Theloop gain comprises an integral plant in conjunction with the motor losscontroller system 101 of FIG. 1. The motor frequency is 1000/6 Hz. Thephase compensation is set to 0 degrees. Almost infinite gain at 1 kHzwill result in the gain crossing 0 dB at 1 kHz (not shown in FIG. 3).The 180° phase lag at 1 kHz in conjunction with any sampling or sensordelays means that the system is likely to be unstable or will have verylittle gain margin.

According to various embodiments and with reference to FIG. 4, the loopgain and phase of an embodiment of motor loss controller system 101 isshown. The loop gain comprises an integral plant in conjunction with themotor loss controller system 101 of FIG. 1. The motor frequency is1000/6 Hz. The gain at 1 kHz results in adequate disturbance rejection.The phase compensation is set to 90° phase lead phase compensation at 1kHz, which compensates for 90° of phase lag in the integral plant. Thus,with the lead compensation, as depicted, the signal no longer dips downto minus 180 degrees phase lag. The loop phase near 1 kHz is 90°advanced relative to FIG. 3, thus 90° of phase margin is depicted,resulting in enhanced stability.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosure. The scope of the disclosure is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “various embodiments”, “oneembodiment”, “an embodiment”, “an example embodiment”, etc., indicatethat the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases are not necessarily referring to the same embodiment.Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is submitted that it iswithin the knowledge of one skilled in the art to affect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described. After reading the description, itwill be apparent to one skilled in the relevant art(s) how to implementthe disclosure in alternative embodiments. Different cross-hatching isused throughout the figures to denote different parts but notnecessarily to denote the same or different materials.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112(f), unless the element is expressly recitedusing the phrase “means for.” As used herein, the terms “comprises”,“comprising”, or any other variation thereof, are intended to cover anon-exclusive inclusion, such that a process, method, article, orapparatus that comprises a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus.

What is claimed is:
 1. A system comprising: a motor loss controllerstructure configured for motor loss reduction, comprising an inputbandshifting stage, an integral controller stage, and an output inversebandshifting stage; wherein inputs to the system are a feedback signal,a motor frequency signal and a control value, wherein the sine of anangular component of a multiple of the motor frequency signal ismultiplied by the feedback signal in the input bandshifting stage toform a first band-shifted feedback signal, wherein the cosine of theangular component of a multiple of the motor frequency signal ismultiplied by the feedback signal in the input bandshifting stage toform a second band-shifted feedback signal, wherein errors in the firstband-shifted feedback signal and the second band-shifted feedback signalare cancelled via integral control in the integral controller stage,wherein an inverse frequency-shift transformation is applied to anoutput of the integral controller stage in the output inversebandshifting stage, and wherein a phase lead compensation is introducedat the multiple of the motor frequency signal.
 2. The system of claim 1,wherein the first band-shifted feedback signal is summed with thecontrol value.
 3. The system of claim 1, wherein the second band-shiftedfeedback signal is summed with the control value.
 4. The system of claim1, wherein the feedback signal comprises at least one of a d-axiscomponent or a q-axis component.
 5. The system of claim 1, wherein thesystem is configured to eliminate distortion in at least one of a d-axisor a q-axis at six times a fundamental frequency.
 6. The system of claim1, wherein the system is configured to eliminate fifth or seventh orderharmonics of a motor current.
 7. The system of claim 1, wherein theinputs to the system further comprise a phase shifting component.
 8. Thesystem of claim 1, wherein a conventional proportional-integralcontroller is implemented in parallel with the motor loss controllerstructure for both a d-axis and a q-axis.
 9. A motor loss controllerconfigured to: band-shift a motor frequency signal by a multiple of afundamental frequency into a parsed sine component and a cosinecomponent and multiply a feedback signal by each of the parsed sinecomponent and the cosine component; perform integral control of acontrol value band-shifted sine component and a control valueband-shifted cosine component, wherein the performing integral controlis configured to at least one of eliminate or reduce a disturbance on anoutput of the motor loss controller by rejecting a DC disturbance in aband-shifted control value; inverse band-shift the sine component backto its original band; inverse band-shift the cosine component back toits original band; sum the inverse band-shifted sine component and theinverse band-shifted cosine component together to result in a controlleroutput; and introduce a phase lead compensation to the inverseband-shifted sine component and the inverse band-shifted cosinecomponent at the multiple of the fundamental frequency.
 10. The motorloss controller of claim 9, further comprising phase shifting theinverse band-shifting of the sine component and phase shifting theinverse band-shifting of the cosine component.
 11. The motor losscontroller of claim 9, wherein the feedback signal comprises at leastone of a d-axis component or a q-axis component.
 12. The motor losscontroller of claim 9, further comprising implementing a conventional PIcontroller in parallel with the motor loss controller for both a d-axisand a q axis of the feedback signal.
 13. The motor loss controller ofclaim 9, wherein the control value band-shifted sine component iscreated by summing the sine component of the band-shifted feedbacksignal with a control value, and wherein the control value band-shiftedcosine component is created by summing the cosine component of theband-shifted feedback signal with the control value.
 14. The motor losscontroller of claim 9, wherein the motor loss controller is configuredto eliminate fifth or seventh order harmonics of a motor current. 15.The motor loss controller of claim 9, wherein the multiple of thefundamental frequency is six times the fundamental frequency.